This application is based on and claims priority to Japanese Patent Application Nos. 11-030,607, filed Feb. 8, 1999, and 11-030,593, filed Feb. 8, 1999, the entire contents of which arc hereby expressly incorporated by reference. A copy of each of these Japanese applications is attached hereto in an appendix.
The present invention generally relates to natural gas compressors. More particularly, the present invention relates to methods and apparatus for fast filling tanks with pressurized natural gases.
Gas storage vessels, such as gas cylinders, bottles or tanks, are commonly filled with gases by charging the gas into the vessel until the desired pressure is reached. It is desirable to fill the vessels as quickly as possible, but it is also important to accurately fill the vessels with the target quantity of gas, such as a quantity associated with a completely filled or charged tank. One problem that makes it difficult to accurately measure the amount of gas in a charged gas vessel is the temperature-pressure relationship of contained gases. By virtue of the gas laws, the pressure exerted by a given volume of gas is directly proportional to its temperature. Accordingly, as the temperature of a gas increases, the pressure of the gas also increases. Thus, when filling gas receiving vessels by pressure measurements, it is important that the gas in the receiving, vessel be at or about a preset or ambient temperature when it approaches its xe2x80x9cfilledxe2x80x9d pressure to ensure that approximately the correct amount of gas is charged into the vessel.
Since it is desirable to fill the gas receiving vessel in the shortest possible time, it is customary to immediately open the fill valve to the wide-open position. This causes an immediate blast of gas to enter the empty vessel, which causes the temperature of the gas being charged into the vessel to rise rapidly as the pressure in the vessel increases. Rapid filling of the vessel can not continue to cause a rapid temperature increase throughout the filling, process, and the initially heated gas cools as additional gas expands (i.e., expansion lowers temperature) into the receiving vessel. However, often the as temperature does not return to the ambient temperature during the filling process and, thus, the pressure within the receiving vessel is elevated above the pressure that the receiving vessel ultimately achieves when it returns to ambient temperature. Thus, without allowing the tank to cool after being filled and then checking its pressure, it is difficult to ensure that the vessel has been completely filled for use in ambient conditions. Such cooling often requires substantial time.
In addition, the temperature of the gas within the tank also increases as the pressure within the tank increases during filling. Accordingly, if the temperature of the gas used to fill the tank is maintained substantially constant during the filling process the tank actually begins to increase in temperature. Thus, this heating problem becomes even more evident as the tank approaches a filled pressure level.
Because service-time of the equipment is valuable and because accuracy of tank filling is important, it would be desirable to fill empty gas vessels with natural gas by a method which does not cause a rapid rise of the temperature of the gas when gas is introduced into an empty vessel and to reduce the heating of the receiving vessel resulting from pressure increases within the vessel. Such a technique should allow the tank to be rapidly filled without the need for cooling the vessel after filling.
Accordingly, one aspect of the present invention involves a natural gas filling apparatus comprising an engine and a compressor. The engine comprises an induction system and an exhaust manifold. The apparatus also comprises an inlet nozzle and a dehumidifier that is connected to the inlet nozzle through a first gas supply pipe. A second gas supply pipe extends between the compressor and the dehumidifier. The dehumidifier comprises a first moisture absorbing filter and a second moisture absorbing filter. A heated air supply is connected to the first filter and the second filter and a heated air return is connected to the induction system. A first switching portion is interposed between the first gas supply pipe, the heated air supply and the first and second moisture absorbing filters, and a second switching portion is interposed between the second gas supply pipe, the heated air return and the first and second moisture absorbing filters. The first portion and the second portion selectively connect the first gas supply pipe and the second gas supply pipe to one of the first filter and the second filter and the heated air supply and the heat air return to the other of the first filter and the second filter. The compressor further comprises multiple compression stages and communicates with a delivery conduit. The delivery conduit connects the compressor to an outlet socket with a gas cooling heat exchanger interposed between at least a portion of the compressor and the delivery conduit. A pressure sensor communicates with the delivery conduit.
Another aspect of the present invention involves a natural gas filling apparatus comprising, an engine and a compressor driven by the engine. The compressor comprises a multiple stage positive displacement compressor and a gas cooling heat exchanger. An outlet valve is adapted to selectively fill removable receiving vessels with compressed gas and a delivery conduit connects the compressor to the outlet valve. A pressure sensor is positioned along the delivery conduit and is in communication with and inputting a pressure signal to a controller. The controller is configured to control an operational characteristic of the compressor when the pressure signal indicates an increase in pressure.
A further aspect of the present invention involves a dehumidifier for use in a natural gas compressor being powered by an internal combustion engine and having an intake system and an exhaust collector. The dehumidifier comprises a gas inlet and a gas outlet. A first branch connects the inlet and the inlet and a second branch connects the inlet and the outlet. A first moisture filter is positioned along the first branch and a second moisture filter is positioned along the second branch. A heated air supply and a heated air exhaust also are collected to the dehumidifier. The heated air exhaust extends between the dehumidifier and is adapted to attach to the intake system. A first three way valve connects the inlet, the supply and the first filter. A second three way valve connects the inlet, the supply and the second filter. A third three way valve connects the outlet, the exhaust and the first filter. A fourth three way valve connects the outlet, the exhaust and the second filter.
Another aspect of the present invention involves a natural gas filling apparatus comprising an engine, a compressor driven by the engine and a gas cooling heat exchanger. The compressor comprises a multiple stage compressor and an outlet valve that is adapted to selectively fill a removable receiving vessel with compressed gas from the compressor. A delivery conduit connects the compressor to the outlet valve. Means for detecting a degree to which the vessel is filled with compressed gas are provided as are means for adjusting a temperature of the gas being delivered to the vessel through the delivery conduit in response to the degree to which the vessel is filled with compressed gas.
A further aspect of the present invention involves a method of fast filling, a container with compressed gas comprising driving a compressor with an engine. The method also involves providing a stream of compressed gas from the compressor to a receiver vessel and monitoring a pressure of the stream of compressed gas. The method further involves decreasing the temperature of the stream of compressed gas as the pressure of the stream of compressed gas increases above a preset pressure.